If your items are less than 1KB in size, then each unit of Read Capacity will give you 1 read/second of capacity and each unit of Write Capacity will give you 1 write/second of capacity. For example, if your items are 512 bytes and you need to read 100 items per second from your table, then you need to provision 100 units of Read Capacity.
Looks like 1KB is the minimum for calculations.
This is currently an undocumented benefit of the query operation, but we will be adding that to our documentation shortly.
Now I'm not sure this would be the ideal solution for such a thing (in fact it probably is not), but it's just the first thing that came to mind. In the grand scheme of things sure that may seem like a trivial amount due to the use case, but we're still more in the realm of a startup where dropping ~$3k/month on the data store alone makes me cringe a little when we have other expenses to account for also. :)
Consider this cost relative to the cost of a trustworthy ops person, plus the capex & opex of running your own reliable & scalable DB.